Make the 'zpool import' command honor the overlay property to allow
filesystems to be mounted on a non-empty directory. As it stands now
this property is only checked by the 'zfs mount' command. Move the
check into 'zfs_mount()` in libzpool so the property is honored for all
callers.
Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#3227
Add a new 'overlay' property (default 'off') that controls whether the
filesystem should be mounted even if the mountpoint is busy or if it
should fail with a 'mountpoint not empty'.
Doing overlay mounts is the default mount behavior on Linux, but not
in ZFS. It have been decided that following the ZFS behavior should
be the default, but this overlay allows for site administrator to
override this decision on a per-dataset basis.
Signed-off-by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes: #2503
4757 ZFS embedded-data block pointers ("zero block compression")
4913 zfs release should not be subject to space checks
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Max Grossman <max.grossman@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Dan McDonald <danmcd@omniti.com>
Approved by: Dan McDonald <danmcd@omniti.com>
References:
https://www.illumos.org/issues/4757https://www.illumos.org/issues/4913https://github.com/illumos/illumos-gate/commit/5d7b4d4
Porting notes:
For compatibility with the fastpath code the zio_done() function
needed to be updated. Because embedded-data block pointers do
not require DVAs to be allocated the associated vdevs will not
be marked and therefore should not be unmarked.
Ported by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#2544
According to the man page, "When the noauto option is set, a dataset
can only be mounted and unmounted explicitly. The dataset is not
mounted automatically when the dataset is created or imported ...."
When cloning a dataset the canmount property was not being honored.
This patch adds the required check to achieve the behavior described
in the man page.
Signed-off-by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#2241
When fetching property values of snapshots, a check against the head
dataset type must be performed. Previously, this additional check was
performed only when fetching "version", "normalize", "utf8only" or "case".
This caused the ZPL properties "acltype", "exec", "devices", "nbmand",
"setuid" and "xattr" to be erroneously displayed with meaningless values
for snapshots of volumes. It also did not allow for the display of
"volsize" of a snapshot of a volume.
This patch adds the headcheck flag paramater to zfs_prop_valid_for_type()
and zprop_valid_for_type() to indicate the check is being done
against a head dataset's type in order that properties valid only for
snapshots are handled correctly. This allows the the head check in
get_numeric_property() to be performed when fetching a property for
a snapshot.
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#2265
This is a continuation of fb5c53ea65:
When /etc/mtab is updated on Linux it's done atomically with
rename(2). A new mtab is written, the existing mtab is unlinked,
and the new mtab is renamed to /etc/mtab. This means that we
must close the old file and open the new file to get the updated
contents. Using rewind(3) will just move the file pointer back
to the start of the file, freopen(3) will close and open the file.
In this commit, a few more rewind(3) calls were replaced with freopen(3)
to allow updated mtab entries to be picked up immediately.
Signed-off-by: John M. Layman <jml@frijid.net>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#2215
Issue #1611
Re-enable the /etc/mtab cache to prevent the zfs command from
having to repeatedly open and read from the /etc/mtab file.
Instead an AVL tree of the mounted filesystems is created and
used to vastly speed up lookups. This means that if non-zfs
filesystems are mounted concurrently the 'zfs mount' will not
immediately detect them. In practice that will rarely happen
and even if it does the absolute worst case would be a failed
mount. This was originally disabled out of an abundance of
paranoia.
NOTE: There may still be some parts of the code which do not
consult the mtab cache. They should be updated to check the
mtab cache as they as discovered to be a problem.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Chris Dunlop <chris@onthe.net.au>
Issue #845
Move the libzfs_fini() after the zpool_log_history() call so the
ZPOOL_HIST_CMD entry can get written.
Fix the handling of saved_poolname in zfsdev_ioctl()
which was broken as part of the stack-reduction work in
a168788053.
Since ZoL destroys the TSD data in which the previously successful
ioctl()'s pool name is stored following every vop, the ZFS_IOC_LOG_HISTORY
ioctl has a very important restriction: it can only successfully write
a long entry following a successful ioctl() if no intervening vops have
been performed. Some of zfs subcommands do perform intervening vops and
to do the logging themselves. At the moment, the "create" and "clone"
subcommands have been modified appropriately.
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#1998
The vast majority of these changes are in Linux specific code.
They are the result of not having an automated style checker to
validate the code when it was originally written. Others were
caused when the common code was slightly adjusted for Linux.
This patch contains no functional changes. It only refreshes
the code to conform to style guide.
Everyone submitting patches for inclusion upstream should now
run 'make checkstyle' and resolve any warning prior to opening
a pull request. The automated builders have been updated to
fail a build if when 'make checkstyle' detects an issue.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#1821
4208 Typo in zfs_main.c: "posxiuser"
Reviewed by: Sonu Pillai <sonu.pillai@delphix.com>
Reviewed by: Will Guyette <will.guyette@delphix.com>
Reviewed by: Eric Diven <eric.diven@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Approved by: Richard Lowe <richlowe@richlowe.net>
References:
https://www.illumos.org/issues/4208illumos/illumos-gate@f38cb554a5
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#1986
3894 zfs should not allow snapshot of inconsistent dataset
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Gordon Ross <gwr@nexenta.com>
References:
https://www.illumos.org/issues/3894illumos/illumos-gate@ca48f36f20
Ported-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1775
3740 Poor ZFS send / receive performance due to snapshot
hold / release processing
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Christopher Siden <christopher.siden@delphix.com>
References:
https://www.illumos.org/issues/3740illumos/illumos-gate@a7a845e4bf
Ported-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1775
Porting notes:
1. 13fe019870 introduced a merge conflict
in dsl_dataset_user_release_tmp where some variables were moved
outside of the preprocessor directive.
2. dea9dfefdd747534b3846845629d2200f0616dad made the previous merge
conflict worse by switching KM_SLEEP to KM_PUSHPAGE. This is notable
because this commit refactors the code, adding a new KM_SLEEP
allocation. It is not clear to me whether this should be converted
to KM_PUSHPAGE.
3. We had a merge conflict in libzfs_sendrecv.c because of copyright
notices.
4. Several small C99 compatibility fixed were made.
Libraries that depend on other libraries should list them in ELF's
DT_NEEDED field so that programs linking to them do not need to specify
those libraries unless they depend on them as well. This is not the case
in the current code and the consequence is that anything that needs a
library must know its dependencies. This is fragile and caused GRUB2's
configure script to break when a dependency was added on libblkid in
libzfs.
This resolves that problem by using LIBADD/LDADD to specify libraries in
Makefile.am instead of LDFLAGS. This ensures that proper DT_NEEDED
entries are generated and prevents GRUB2's configure script from
breaking in the presence of a libblkid dependency. This also removes
unneeded dependencies from various files.
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1751
2882 implement libzfs_core
2883 changing "canmount" property to "on" should not always remount dataset
2900 "zfs snapshot" should be able to create multiple, arbitrary snapshots at once
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Chris Siden <christopher.siden@delphix.com>
Reviewed by: Garrett D'Amore <garrett@damore.org>
Reviewed by: Bill Pijewski <wdp@joyent.com>
Reviewed by: Dan Kruchinin <dan.kruchinin@gmail.com>
Approved by: Eric Schrock <Eric.Schrock@delphix.com>
References:
https://www.illumos.org/issues/2882https://www.illumos.org/issues/2883https://www.illumos.org/issues/2900illumos/illumos-gate@4445fffbbb
Ported-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#1293
Porting notes:
WARNING: This patch changes the user/kernel ABI. That means that
the zfs/zpool utilities built from master are NOT compatible with
the 0.6.2 kernel modules. Ensure you load the matching kernel
modules from master after updating the utilities. Otherwise the
zfs/zpool commands will be unable to interact with your pool and
you will see errors similar to the following:
$ zpool list
failed to read pool configuration: bad address
no pools available
$ zfs list
no datasets available
Add zvol minor device creation to the new zfs_snapshot_nvl function.
Remove the logging of the "release" operation in
dsl_dataset_user_release_sync(). The logging caused a null dereference
because ds->ds_dir is zeroed in dsl_dataset_destroy_sync() and the
logging functions try to get the ds name via the dsl_dataset_name()
function. I've got no idea why this particular code would have worked
in Illumos. This code has subsequently been completely reworked in
Illumos commit 3b2aab1 (3464 zfs synctask code needs restructuring).
Squash some "may be used uninitialized" warning/erorrs.
Fix some printf format warnings for %lld and %llu.
Apply a few spa_writeable() changes that were made to Illumos in
illumos/illumos-gate.git@cd1c8b8 as part of the 3112, 3113, 3114 and
3115 fixes.
Add a missing call to fnvlist_free(nvl) in log_internal() that was added
in Illumos to fix issue 3085 but couldn't be ported to ZoL at the time
(zfsonlinux/zfs@9e11c73) because it depended on future work.
3098 zfs userspace/groupspace fail without saying why when run as non-root
Reviewed by: Eric Schrock <eric.schrock@delphix.com>
Approved by: Richard Lowe <richlowe@richlowe.net>
References:
https://www.illumos.org/issues/3098illumos/illumos-gate@70f56fa693
Ported-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#1596
Remove all of the generated autotools products from the repository
and update the .gitignore files accordingly.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#718
1796 "ZFS HOLD" should not be used when doing "ZFS SEND" from a read-only pool
2871 support for __ZFS_POOL_RESTRICT used by ZFS test suite
2903 zfs destroy -d does not work
2957 zfs destroy -R/r sometimes fails when removing defer-destroyed snapshot
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Approved by: Eric Schrock <Eric.Schrock@delphix.com>
References:
https://www.illumos.org/issues/1796https://www.illumos.org/issues/2871https://www.illumos.org/issues/2903https://www.illumos.org/issues/2957
Ported by: Martin Matuska <martin@matuska.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: Matt Ahrens <matt@delphix.com>
Reviewed by: George Wilson <George.Wilson@delphix.com>
Reviewed by: Bill Pijewski <wdp@joyent.com>
Reviewed by: Richard Elling <richard.elling@richardelling.com>
Approved by: Richard Lowe <richlowe@richlowe.net>
References:
https://www.illumos.org/issues/2635
Ported by: Martin Matuska <martin@matuska.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#717
Currently, zvols have a discard granularity set to 0, which suggests to
the upper layer that discard requests of arbirarily small size and
alignment can be made efficiently.
In practice however, ZFS does not handle unaligned discard requests
efficiently: indeed, it is unable to free a part of a block. It will
write zeros to the specified range instead, which is both useless and
inefficient (see dnode_free_range).
With this patch, zvol block devices expose volblocksize as their discard
granularity, so the upper layer is aware that it's not supposed to send
discard requests smaller than volblocksize.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#862
1644 add ZFS "clones" property
1645 add ZFS "written" and "written@..." properties
1646 "zfs send" should estimate size of stream
1647 "zfs destroy" should determine space reclaimed by
destroying multiple snapshots
1708 adjust size of zpool history data
References:
https://www.illumos.org/issues/1644https://www.illumos.org/issues/1645https://www.illumos.org/issues/1646https://www.illumos.org/issues/1647https://www.illumos.org/issues/1708
This commit modifies the user to kernel space ioctl ABI. Extra
care should be taken when updating to ensure both the kernel
modules and utilities are updated. This change has reordered
all of the new ioctl()s to the end of the list. This should
help minimize this issue in the future.
Reviewed by: Richard Lowe <richlowe@richlowe.net>
Reviewed by: George Wilson <gwilson@zfsmail.com>
Reviewed by: Albert Lee <trisk@opensolaris.org>
Approved by: Garrett D'Amore <garret@nexenta.com>
Ported by: Martin Matuska <martin@matuska.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#826Closes#664
The end_writeback() function was changed by moving the call to
inode_sync_wait() earlier in to evict(). This effecitvely changes
the ordering of the sync but it does not impact the details of
the zfs implementation.
However, as part of this change end_writeback() was renamed to
clear_inode() to reflect the new semantics. This change does
impact us and clear_inode() now maps to end_writeback() for
kernels prior to 3.5.
Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#784
The vmtruncate_range() support has been removed from the kernel in
favor of using the fallocate method in the file_operations table.
Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #784
The export_operations member ->encode_fh() has been updated to
take both the child and parent inodes. This interface used to
take the child dentry and a bool describing if the parent is needed.
NOTE: While updating this code I noticed that we do not currently
cleanly handle the case where we're passed a connectable parent.
This code should be audited to make sure we're doing the right thing.
Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #784
Currently, zpool online -e (dynamic vdev expansion) doesn't work on
whole disks because we're invoking ioctl(BLKRRPART) from userspace
while ZFS still has a partition open on the disk, which results in
EBUSY.
This patch moves the BLKRRPART invocation from the zpool utility to the
module. Specifically, this is done just before opening the device in
vdev_disk_open() which is called inside vdev_reopen(). This requires
jumping through some hoops to get to the disk device from the partition
device, and to make sure we can still open the partition after the
BLKRRPART call.
Note that this new code path is triggered on dynamic vdev expansion
only; other actions, like creating a new pool, are unchanged and still
call BLKRRPART from userspace.
This change also depends on API changes which are available in 2.6.37
and latter kernels. The build system has been updated to detect this,
but there is no compatibility mode for older kernels. This means that
online expansion will NOT be available in older kernels. However, it
will still be possible to expand the vdev offline.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#808
FreeBSD #xxx: Dramatically optimize listing snapshots when user
requests only snapshot names and wants to sort them by name, ie.
when executes:
# zfs list -t snapshot -o name -s name
Because only name is needed we don't have to read all snapshot
properties.
Below you can find how long does it take to list 34509 snapshots
from a single disk pool before and after this change with cold and
warm cache:
before:
# time zfs list -t snapshot -o name -s name > /dev/null
cold cache: 525s
warm cache: 218s
after:
# time zfs list -t snapshot -o name -s name > /dev/null
cold cache: 1.7s
warm cache: 1.1s
NOTE: This patch only appears in FreeBSD. If/when Illumos picks up
the change we may want to drop this patch and adopt their version.
However, for now this addresses a real issue.
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #450
torvalds/linux@adc0e91ab1 introduced
introduced d_make_root() as a replacement for d_alloc_root(). Further
commits appear to have removed d_alloc_root() from the Linux source
tree. This causes the following failure:
error: implicit declaration of function 'd_alloc_root'
[-Werror=implicit-function-declaration]
To correct this we update the code to use the current d_make_root()
interface for readability. Then we introduce an autotools check
to determine if d_make_root() is available. If it isn't then we
define some compatibility logic which used the older d_alloc_root()
interface.
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#776
The mode argument of iops->create()/mkdir()/mknod() was changed from
an 'int' to a 'umode_t'. To prevent a compiler warning an autoconf
check was added to detect the API change and then correctly set a
zpl_umode_t typedef. There is no functional change.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#701
Add support for the `zfs list -t snap` alias which is available under
Oracle Solaris 11.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#640
For consistency, and because it's handy, add the 'zfs snap' alias which
was introduced by Oracle Solaris 11. This includes an update to the
man page to reflect all the available alias (snap, umount, and recv).
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#640
Caught by lint, this permission change was accidentally introduced
by commit 42cb3819f1. Restore the
correct permissions and while I'm at it add a missing whack-bang
to config/ltmain.sh.
lint: executable-not-elf-or-script: zpool_main.c zfs_main.c
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#620
Allow rigorous (and expensive) tx validation to be enabled/disabled
indepentantly from the standard zfs debugging. When enabled these
checks ensure that all txs are constructed properly and that a dbuf
is never dirtied without taking the correct tx hold.
This checking is particularly helpful when adding new dmu consumers
like Lustre. However, for established consumers such as the zpl
with no known outstanding tx construction problems this is just
overhead.
--enable-debug-dmu-tx - Enable/disable validation of each tx as
--disable-debug-dmu-tx it is constructed. By default validation
is disabled due to performance concerns.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Add support for the .zfs control directory. This was accomplished
by leveraging as much of the existing ZFS infrastructure as posible
and updating it for Linux as required. The bulk of the core
functionality is now all there with the following limitations.
*) The .zfs/snapshot directory automount support requires a 2.6.37
or newer kernel. The exception is RHEL6.2 which has backported
the d_automount patches.
*) Creating/destroying/renaming snapshots with mkdir/rmdir/mv
in the .zfs/snapshot directory works as expected. However,
this functionality is only available to root until zfs
delegations are finished.
* mkdir - create a snapshot
* rmdir - destroy a snapshot
* mv - rename a snapshot
The following issues are known defeciences, but we expect them to
be addressed by future commits.
*) Add automount support for kernels older the 2.6.37. This should
be possible using follow_link() which is what Linux did before.
*) Accessing the .zfs/snapshot directory via NFS is not yet possible.
The majority of the ground work for this is complete. However,
finishing this work will require resolving some lingering
integration issues with the Linux NFS kernel server.
*) The .zfs/shares directory exists but no futher smb functionality
has yet been implemented.
Contributions-by: Rohan Puri <rohan.puri15@gmail.com>
Contributiobs-by: Andrew Barnes <barnes333@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#173
The 'zfs list' and 'zpool list' commands output the message
'no datasets/pools available' to stdout. This should go to
stderr and only the available datasets/pools should go to
stdout. Returning nothing to stdout is expected behavior
when there is nothing to list.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#581
Allow a source rpm to be rebuilt with debugging enabled. This
avoids the need to have to manually modify the spec file. By
default debugging is still largely disabled. To enable specific
debugging features use the following options with rpmbuild.
'--with debug' - Enables ASSERTs
# For example:
$ rpmbuild --rebuild --with debug zfs-modules-0.6.0-rc6.src.rpm
Additionally, ZFS_CONFIG has been added to zfs_config.h for
packages which build against these headers. This is critical
to ensure both zfs and the dependant package are using the same
prototype and structure definitions.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
DISCARD (REQ_DISCARD, BLKDISCARD) is useful for thin provisioning.
It allows ZVOL clients to discard (unmap, trim) block ranges from
a ZVOL, thus optimizing disk space usage by allowing a ZVOL to
shrink instead of just grow.
We can't use zfs_space() or zfs_freesp() here, since these functions
only work on regular files, not volumes. Fortunately we can use the
low-level function dmu_free_long_range() which does exactly what we
want.
Currently the discard operation is not added to the log. That's not
a big deal since losing discard requests cannot result in data
corruption. It would however result in disk space usage higher than
it should be. Thus adding log support to zvol_discard() is probably
a good idea for a future improvement.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Currently only the (FALLOC_FL_PUNCH_HOLE) flag combination is
supported, since it's the only one that matches the behavior of
zfs_space(). This makes it pretty much useless in its current
form, but it's a start.
To support other flag combinations we would need to modify
zfs_space() to make it more flexible, or emulate the desired
functionality in zpl_fallocate().
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #334
The Linux block device queue subsystem exposes a number of configurable
settings described in Linux block/blk-settings.c. The defaults for these
settings are tuned for hard drives, and are not optimized for ZVOLs. Proper
configuration of these options would allow upper layers (I/O scheduler) to
take better decisions about write merging and ordering.
Detailed rationale:
- max_hw_sectors is set to unlimited (UINT_MAX). zvol_write() is able to
handle writes of any size, so there's no reason to impose a limit. Let the
upper layer decide.
- max_segments and max_segment_size are set to unlimited. zvol_write() will
copy the requests' contents into a dbuf anyway, so the number and size of
the segments are irrelevant. Let the upper layer decide.
- physical_block_size and io_opt are set to the ZVOL's block size. This
has the potential to somewhat alleviate issue #361 for ZVOLs, by warning
the upper layers that writes smaller than the volume's block size will be
slow.
- The NONROT flag is set to indicate this isn't a rotational device.
Although the backing zpool might be composed of rotational devices, the
resulting ZVOL often doesn't exhibit the same behavior due to the COW
mechanisms used by ZFS. Setting this flag will prevent upper layers from
making useless decisions (such as reordering writes) based on incorrect
assumptions about the behavior of the ZVOL.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
zvol_write() assumes that the write request must be written to stable storage
if rq_is_sync() is true. Unfortunately, this assumption is incorrect. Indeed,
"sync" does *not* mean what we think it means in the context of the Linux
block layer. This is well explained in linux/fs.h:
WRITE: A normal async write. Device will be plugged.
WRITE_SYNC: Synchronous write. Identical to WRITE, but passes down
the hint that someone will be waiting on this IO
shortly.
WRITE_FLUSH: Like WRITE_SYNC but with preceding cache flush.
WRITE_FUA: Like WRITE_SYNC but data is guaranteed to be on
non-volatile media on completion.
In other words, SYNC does not *mean* that the write must be on stable storage
on completion. It just means that someone is waiting on us to complete the
write request. Thus triggering a ZIL commit for each SYNC write request on a
ZVOL is unnecessary and harmful for performance. To make matters worse, ZVOL
users have no way to express that they actually want data to be written to
stable storage, which means the ZIL is broken for ZVOLs.
The request for stable storage is expressed by the FUA flag, so we must
commit the ZIL after the write if the FUA flag is set. In addition, we must
commit the ZIL before the write if the FLUSH flag is set.
Also, we must inform the block layer that we actually support FLUSH and FUA.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
